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Versatile Car Scrolling Display, Part 1

This project started out as a digital dashboard display but has grown and can be used in any measurement or data logging application where you have 9-12V DC available. It can monitor up to six signals and display up to 10 computed values in a scrolling or static readout on a 7 x 15 dot matrix LED display.

By Mauro Grassi

Main Features & Specifications

  • Can be powered from 9-12V DC or from a USB port (5V).
  • Two Frequency/Duty Cycle Inputs with frequency up to 10kHz.
  • Positive Duty Cycle Range: 0-100%.
  • Four Voltage/Resistance Inputs Plus Battery Voltage (the latter has its own channel).
  • Voltage Range: 0-16V (greater or smaller ranges possible by changing one resistor).
  • Sensitivity with 16V scale: approx. 16mV.
  • Best Sensitivity: approx. 5mV (requires changing one resistor and recalibrating using the supplied PC software).
  • Two output channels to drive external relays or buzzers.
  • Up to 10 displayed variables.
  • Averaging or direct acquisition mode for each variable.
  • Screen dimming on ambient light with adjustable sensitivity and selectable minimum brightness.
  • 7 x 15 dot matrix LED display (scrolling or static display).
  • Static display of up to 4 digits (floating point)
  • Selectable scrolling speed.
  • On screen limit warnings for each variable in the static display mode.
  • Software calibration using polynomial interpolation.
  • Persistent settings stored in non-volatile memory.
  • Easily load and store previous settings to file on your computer.
  • Easily load and store different calibration point files on your computer.
  • All settings changeable using the USB port and PC host program.
  • Data logging via the USB port; selectable variable update frequency from 0.1-8Hz; can collect 1000s of samples to a PC’s hard drive.
  • So what’s a scrolling display? You really need a short video to show what this project does. The readout continually "scrolls" from left to right, displaying one, two and up to 10 computed values from up to six different signals. Each value is preceded by its description, such as battery voltage, temperature, duty cycle and so on. If you want to focus on one reading, pressing the sole pushbutton will make the display static.

    Click for larger image
    Fig.1: block diagram of the Car Scrolling Display. A PIC 18F4550 microcontroller is at the heart of the project. It processes various inputs, drives the dot matrix display, manages the USB connection and drives the two outputs.

    Anyway, let’s just give a sample of what this project can do:

  • Measure Engine Temperature – have
    a relay switch on above a preset temperature.

  • Measure Fuel Injector Duty – have a relay switch if the duty cycle is too high or too low.

  • Measure Engine RPM – have a relay switch on at a preset RPM (perhaps to indicate when to change gear).

  • Measure Throttle Position and Delta Throttle Position – if the accelerator pedal is pressed too abruptly, a relay can be made to switch on this condition.

  • Measure Speed – have a relay switch if the speed is too high or too low.

  • Measure Fuel Tank Level as a percentage of full tank – have a relay switch on or off if the level is too high or too low.

  • Measure Battery Voltage – have a relay switch on if the voltage is too high or too low.

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